In joining an annular member and a shaft member (axle) to each other, it has been customary to press fit one end of the shaft member into a bore of the annular member so as to produce a press fit, that is a fit with an interference of a negative gap, so as to be secured to each other in axial and rotational directions. However, with such press fit when performed under dry frictional conditions, it is extremely difficult or occasionally impossible to perform the press fit through scoring of the mating surfaces. If the shaft member is forced into the annular member, the alignment of the annular member about the axis is deteriorated (tolerance enlarged).
There is also known a manner of providing smooth press fit free of scoring by directly utilizing an oil, such as rust-preventing oil, applied to the surface of the shaft member, at the time of press fitting. However, with this manner, it may occur that an excess amount of oil remains as an oil film on the overall mating surfaces to weaken the jointing force between the annular member and the shaft member to cause idle rotation or axial shifting (generally slide) of the annular member relative to the shaft member.
As hereinabove mentioned, there is discrepancy in the prior art. Namely, with the technique for an enhanced jointing force, it becomes difficult to perform the press fitting operation, while the misalignment of the annular member about its axis is enlarged. On the other hand, with the manner for improving the precision in axial alignment, the jointing force is lowered.
Along this line, the JP U.M. KOKAI Publication 63-115926 (1988) discloses an artifice in which a recess is provided on at least one of the outer circumferential surface of the shaft member or the inner peripheral surface of a bore of the annular member, an oil film of the rust-preventing oil remaining on the mating surfaces (more precisely, mating clearance) are interrupted (or blocked) and scraped off by the edge of the recess upon press fitting the shaft member, and the scraped rust-preventing oil is stored within the recess.